1. Field of the Invention
The present invention generally relates to systems and methods for controlling emergency lighting where emergency lights turn on when main source of power goes out. More particularly, the present invention relates to lighting systems and methods for controlling emergency lighting to conserve energy utilized by the emergency light, while maintaining good visibility of the emergency lighting.
2. Discussion of the Background
An important consideration for emergency lighting is visibility. For example, U.S. Pat. No. 7,234,844 to Bolta et al., the entire disclosure of which is hereby incorporated by reference, describes emergency lighting fixtures that incorporate light emitting diode (LED) lighting sources made with scotopically rich primary colors which increase perceived light even under a low lumen output, because the human eye responds more to blue light and less to yellow/red light. That is, Bolta et al. describe various blends and configurations of color LEDs for emergency lighting that operate at reduced lumen output while increasing the eye's ability to respond to low levels of light by the use of primary scotopic color of LEDs.
Another important consideration in any lighting application is conservation of energy. For emergency lighting conservation of energy becomes even more critical because emergency lighting is often operated using back-up battery power, or other emergency power sources having a limited available power over a given duration of time. Thus, it is desirable to reduce power consumption by emergency lighting so as to extend the duration of available emergency lighting. However, the reduction of power must be mitigated by potentially reduced visibility as the light dim in such during emergency lighting application.
Conventional emergency light systems that utilize filament based lighting sources (light bulb) not only dim, but also shifts in color temperature from a white light to a much more red light, when power reduced. Since human eyes respond better to colors in the blue/green spectrum than in the red spectrum, a filament bulb will not only get dimmer, but will be perceived as dimmer than it actually is. Accordingly, while power consumption is reduced, so is the visibility.
On the other hand, while conventional LED-based emergency lighting systems, for example as described in Bolta et al, operate at a reduced power compared to normal lighting conditions, this reduced power is maintained at a constant level not allowing for further power conservation to be achieved.